The present invention relates to an automatic speed control system for a motor vehicle.
More specifically, the present invention provides necessary and substantial improvement to the type of vehicle speed control system disclosed in U.S. Pat. No. 3,441,104. The system comprises a speed sensor or transducer which modulates intake manifold vacuum in accordance with vehicle speed to produce an output pressure which directly corresponds to the vehicle speed. This pressure is applied to a diaphragm assembly which controls the engine fuel control member. When the vehicle speed increases the amount of fuel for combustion is decreased and vice-versa so that the vehicle is controlled to move at a predetermined speed regardless of vehicle load.
Whereas the system operates effectively under mild driving conditions, fuel control alone is not sufficient to limit the vehicle speed to the predetermined value when the vehicle is heavily loaded and moving down a steep grade. In other words, engine braking alone is not sufficient to slow down the vehicle by the required amount. In such a case, the vehicle operator must override the system using the manual brake pedal. However, depression of the brake pedal deenergizes the automatic control system returning the control of the vehicle to the operator entirely. This situation is dangerous since control is returned to the operator under extreme driving conditions after a period of automatic control. It may take as much as a few seconds for the driver to get the feeling of the vehicle under such conditions so that he may respond effectively. During these few seconds control of the vehicle may be lost resulting in a tragic accident.